The CFD–DEM coupled approach was used to simulate the complex gas–solid reacting flows in fluid catalytic cracking (FCC) processes accommodated in riser or downer reactors. Considering the solid catalyzed gas-phase reactions, the model particularly incorporated the descriptions for heat transfer behaviors between particles and between gas and particles, the instantaneous catalyst deactivation, and the lumped kinetics in the gas phase for FCC process, together with the governing equations for the hydrodynamics. The distinct advantage of the present approach is that the catalyst activity can be calculated in time by tracking the history of the particle movement with the occurrence of heat transfer and chemical reactions. The simulation results captured the major features of FCC process very well either in riser or in downer, which had reasonable agreement with the experimental data in the literature. The reduced selectivity to the desired intermediate products in risers, especially under high catalyst-to-oil ratios, can be clearly understood from the simulated backmixing behavior of solid catalysts and the deactivation of catalysts at different locations in the reactor, which caused the non-ideal reaction progress inside the reactor space. It can be concluded that this type of modeling approach forms a solid basis for the cross-scale modeling of general multi-phase catalytic reacting flows.